The following invention relates to a system which may be connected to conventional AC wiring for monitoring electrical energy usage of individual appliances used in a residence and for displaying such information in a plurality of formats selectable by a user.
With the rising cost of home energy use, especially electrical power, it has become desirable to know the quantity of electrical power used by various household appliances so that inefficient uses of electricity can be eliminated. Since home budget planning to an extent depends upon the amount of energy used during different periods such as time of day, day of the week, or season of the year, it would be advantageous to know which time periods were responsible for the maximums and minimums of energy usage, and which particular appliances contributed most heavily during those particular periods to the total amount of energy used. While it is possible to obtain a monthly, daily or weekly total for aggregate home energy use by reading the outside utility meter, such a practice is awkward and cumbersome. Furthermore, the only information that can be obtained from the utility meter is the total energy use of the entire residence. Obviously it cannot be determined from the utility meter which particular appliances contribute most heavily to the total amount of energy usage within any given time frame.
In the past, systems have been available for automatically controlling certain household appliances from a central location. These systems typically use a power line modem which is a transmitter/receiver capable of operating over conventional AC 120/240-volt wiring. In addition to the modem, these systems include a switch for controlling the operation of the appliance which is activated or deactivated by a central control unit. Examples of this type of system are shown in the U.S. Pat. Nos. 4,174,517 to Mandell and 4,418,333 to Schwarzbach. In both of these systems a control unit may be programmed to initiate certain functions within various appliances depending upon the time of day. For example, lights may be programmed to automatically turn on at dark and a coffee maker may be programmed to automatically turn on at a given hour in the morning. Neither the Schwarzbach nor the Mandell system, however, provides any means for monitoring energy usage of the various appliances or devices connected to either system.
Residential energy monitoring systems have been proposed for use by utility companies for remotely and automatically monitoring the aggregate household energy usage of a plurality of homes within a given area. These systems are intended to obviate the need for "meter readers" who personally inspect the utility meters of residences and record monthly or bimonthly energy use. Remote automatic meter reading systems typically transmit power usage information over telephone lines, power lines or by radio communication link. The energy metering devices proposed for these systems, however, consist usually of a retrofit device or circuit intended to be used with or connected to the utility meter located outside the dwelling. There are, for example, optical encoders which "read" the decade dials of a conventional utility grade power meter and such a system is shown in Calabro U.S. Pat. No. 3,900,842. Another type of device uses a digital counting technique responsive to the shaft revolutions of a conventional utility power meter as shown in Bruner U.S. Pat. No. 3,747,068. Another type of system, disclosed in Ward U.S. Pat. No. 4,350,980, uses an optical method for scanning the revolutions of the meter wheel of a standard electric meter and generating digital pulses which are then induced in the electric power cables of the meter to provide data at existing power outlets within the home which may be recorded by a receiving device plugged into an outlet. The principal drawback of all of the foregoing systems is that the energy consumption data is extracted solely from the utility meter, and as such does not provide any information regarding energy consumption of individual appliances or units within the household.
What is needed, therefore, is a system capable of operating in conjunction with standard AC household wiring such that energy use information from selected appliances may be transmitted over the internal building wiring to a master control station, and including a metering device for each of the appliances which is capable of measuring power usage independent of the outside utility meter.